Method for encoding and decoding moving picture signals

ABSTRACT

A method for encoding and decoding digital moving picture signals which can decode subframes appropriately in relation to time if a part of a bit stream is missing or an error occurs in the bit stream, and can suppress degradation of a reproduced picture if decoding of a subframe including a picture in motion in relation to time becomes unfeasible. In the method for encoding and decoding digital moving picture signals of this invention, information for one frame is encoded correspondingly to a spatial hierarchy of a frame, subframes and blocks. A subframe time position number and a subframe space number are attached to an identifier of each of the subframe, thereby resuming appropriate decoding of the subframes immediately after a trouble if an error occurs. The subframe identifiers are placed at a certain interval in the bit stream so as to give a smaller size to a subframe including a block which is in motion and difficult to be encoded, thereby suppressing degradation of a reproduced picture if decoding of the subframe becomes unfeasible.

BACKGROUND OF THE INVENTION

Notice: More than one reissue application has been filed for the reissueof U.S. Pat. No. 5,937,095. The reissues applications are applicationNos. 10/662,949 which is a continuation of 09/925,423 (the presentapplication).

(1) Field of the Invention

The present invention relates to a method for encoding and decodingdigital moving picture signals for use in TV phones, TV conferences andthe like.

(2) Description of the Prior Art

In a general method for encoding digital moving picture signals, a frameof inputted moving picture is divided into plural blocks each composedof N×M pixels, and processes of motion detection, prediction, orthogonaltransform, quantization, variable length coding, etc. are conducted oneach block.

In a general method for decoding digital motion picture signals, blockseach composed of N×M pixels are regenerated in a reverse procdyreprocedure, that is, processes of variable length decoding, reversequantization, reverse orthogonal transform, motion compensation, etc.

The above general encoding method and decoding method for encoding anddecoding digital moving picture signals enable removal of redundancycontained in moving picture signals, and efficient communication andstorage of a moving picture with less information.

In the general encoding method and decoding method for encoding anddecoding digital moving picture signals, the processes are conducted oneach pixel block, as stated above. It is general that a set of pixelblocks forms a subframe and a set of subframes forms a frame, which areunits processed in the general encoding and decoding method.

Hereinafter, encoding and decoding of each block, subframe and framewill be described by way of an example of a general encoding anddecoding method for encoding and decoding digital moving picture signalswith reference to ITU-T Recommendation H.261 (hereinafter, referredsimply H.261) made on March, 1993.

H.261 defines an encoding method and a decoding method for encoding anddecoding luminance signals and color difference signals, separately, ofdigital moving picture signals. However, description will be made ofonly the luminance signals, for the sake of convenience. Basically, theencoding method and decoding method for encoding and decoding theluminance signals are not different from those for the color differencesignals.

As shown in FIG. 1, one frame 101 of digital moving picture signals iscomposed of 352×288 pixels according to H.261. The frame 101 is dividedinto twelve subframes 102 called GOBs (Group of Blocks) each composed of176×48 pixels (hereinafter, the subframe in the description of the priorart will be referred a GOB). Further, the GOB 102 (subframe) is dividedinto thirty three blocks 103 called macro blocks each composed of 16×16pixels.

The encoding method according to H.261 defines that encoded informationfor one frame is corresponded to a spatial hierarchical structure suchas the frame 101, GOBs 102 and macro blocks 103 described above, asshown in FIG. 2.

In FIG. 2, a part enclosed in a rectangle shows encoded information, andthe number of coding bits is shown under each of the rectangles. In FIG.2, arrows show linkages of the encoded information. A series of encodedmoving picture signal sequences as this is called a bit stream 104.

In the bit stream 104 according to H.261 shown in FIG. 2, a partincluding all encoded information for one macro block 103 is called amacro block layer 103S, a part including all encoded information foronce GOB 102 is called a GOB layer 102S, and a part including allencoded information for one frame 101 is called a frame layer 101S.

Meanings of the encoded information in each of the layers shown in FIG.2 are given below:

Frame Layer 101S

PSC (20 bits): a frame identifier 105; a unique code by which anencoding method can be always identified, expressed as “0000 0000 00000000 0001”;

TR (5 bits): a frame number 106; indicating a time position in whichthis frame 101 should be displayed;

PTYPE (6 bits): frame type information 107; various information aboutthe frame 101;

PEI (1 bit): extension data insertion information 108; a flagrepresenting presence of following PSPARE 109;

PSPARE (8 bits): extension data; GOB layer 102S (subframe)

GBSC (16 bits): a GOB identifier 110; a unique code by which a decodingmethod can be always identified, expressed as “0000 0000 0000 0000”;

GN (4 bits): a GOB number 111; indicating a spatial position of this GOB102 within the frame 101;

GQUNAT (5 bits): quantization characteristics information 112;indicating a quantization characteristic when a macro block 103 in theGOB 102 is encoded;

GEI (1 bit): extension data insertion information 113; a flagrepresenting presence of following GSPARE 114;

GSPARE (8 bits): extension data 114.

Incidentally, the encoded information 115 of the macro block layer whichis the lowest hierarchy in FIG. 2 is generated in the encoding method ofmotion detection, prediction, orthogonal transform, quantization,variable length coding, etc., as described before, whose coding bitnumber is not fixed. The number of coding bits of the macro block layer103S, in general, increases if a spatial level of pixels included in themacro block 103 changes largely or a time level of pixels included inthe macro block 103 having the same spatial positions changes largely.Such macro block 103, is hereinafter, referred a macro block 103 whichis difficult to be encoded.

To the contrary, if a level of pixels included in the macro block 103 issteady in relation to space and time, the number of coding bits of themacro block layer 103S remarkably decreases, or sometimes becomes zero.Such macro block 103 is hereinafter referred a macro block 103 which iseasy to be encoded.

In the decoding method according to H.261, the PSC 105 which is anidentifier of the frame layer 101S is first found out from the bitstream 104. Incidentally, in a state where a decodable code has beensuccessfully found out it is said that synchronization is established.When the PSC 105 is found out from the bit stream and synchronization ofthe frame layer 101S is established, it can be identified that the bitstream 104 until the next PCS 105 appears is encoded information for oneframe. Further, a time position in which the frame 101 composed of352×288 pixels obtained by decoding the bit stream 104 for that oneframe can be obtained by examining the frame number 106 following thePSC 105.

After the establishment of the frame layer, a GBSC 110 that is anidentifier of the GOB layer 102S is found out from the following bitstream 104 in the encoding method according to H.261. Whensynchronization of the GBSC layer is established, it can be identifiedthat the bit stream 104 until the next GBSC 110 appears is encodedinformation for one GOB 102. Further, a spatial position of the GOB 102composed of 176×48 pixels obtained by decoding the bit stream 104 forthat one GOB 102 in a frame 101, in which the GOB 102 should be placed,can be obtained by examining a GN 111 which is a GOB number followingthe GBSC 110.

In the decoding method according to H.261, a bit stream 104 of afollowing macro block layer 103S is decoded after the establishment ofthe GOB layer 102s. The decoding method of the macro block layer 103S isa procedure to regenerate a macro block 103 composed of 16×16 pixels inprocesses of variable length decoding, reverse quantization, reverseorthogonal transform, motion compensation, etc., as described before. Itshould be here noted that the macro block layer 103S has no unique codeby which a decoding method can be always identified dissimilarly to thePSC 105 or BGSC 110, and encoded information of each macro block iscomposed of undefined length bits of a variable length code.

As shown in FIG. 3, in the GOB (subframe) layer 102S, the encodedinformation from the first macro block 115, to the thirty third macroblock 115 ₃₃ is expressed as a series of variable length codes without aunique code. If decoding of the macro block encoded information isinitiated from a point indicated by A in FIG. 3, and successivelyconducted in the order of the first, the second, . . . the nth, . . .the thirty third macro blocks, it is possible to regenerate all themacro blocks 103 in the GOB layer 102S. However, if the decoding of themacro block encoded information is initiated from a point indicated by Bor C in FIG. 3, it is impossible to identify a point from which encodedinformation 115 of one macro block starts, which leads to a failure ofestablishing synchronization. In which case, the decoding andregenerating all macro blocks 103 become unfeasible until the next GBSC110 appears. In other words, the GBSC 110 also represents a startingpoint of decoding the macro block layer 103S.

Finally, in the decoding method according to H.261, the GOB 102 which isa set of regenerated macro blocks 103 is placed in a spatial positionwithin a frame 101 directed by GN 111, and the frame 100 which is a setof the regenerated GOBs 102 is placed in a time position directed by TR106.

As above, it is possible to decode one frame 101 of digital movingpicture correctly in relation to space and time according to H.261.

However, the above general method for encoding and decoding digitalmoving picture signals has a drawback that if a part of a bit stream 104lacks is lacking or an error occurs therein, it might be impossible toaccurately decode all subframes (GOBs) 102 in relation to time untilsynchronization of the next frame layer 101S is established.

The reason of the above is that codes which can be identified at alltimes in the bit stream 104 are only the PSC 105 which is a frameidentifier and the GBSC 110 which is a subframe identifier in thegeneral decoding method. If a part of the bit stream 104 lacks or anerror occurs therein, it is impossible to recover synchronization of thedecoding until the next GBSC 110 appears so that the decoding becomesunfeasible. Even if the next GBSC 110 appears, the bit stream 104 ofthat subframe layer 102S cannot be correctly decoded in relation totime. This will be understood from FIG. 4.

FIG. 4 shows an example where the fifth GOB 102 ₅ in the nth frame 110nthrough the sixth GOB 102 ₆ in the (n+1)th frame 101 _(n−1) 101 _(n+1)cannot be decoded in relation to time due to lackslacking portions orerrors of the bit stream 104 occurring in burst. In this example, notonly the PSC 105 corresponding to the (n+1)th frame in relation to timebut also the following TR 106 are missed or in error. It is thereforepossible to correctly decode the GOB 102 ₇ in relation to space byestablishing synchronization from the GBSC 110 corresponding to theseventh GOB 102 ₇ in the (n+1)th frame 101 _(n+1) in relation to timeand decoding the following GN 111, but impossible to specify whetherthis GOB 102 ₇ positions in the nth frame or in the (n+1)th frame inrelation to time.

In terms of decoding of the eighth GOB 102 ₈ through the twelfth GOB 102₁₂ in the (n+1)th frame in relation to time, it is impossible to specifywhether these GOBs 102 position in the nth frame or in the (n+1)th framein relation to time.

In consequence, if a part of the bit stream 104 is missed missing or anerror occurs therein, it becomes impossible to correctly decode all GOBs102 in relation to time until synchronization of the next frame layer101 ₅ is established.

Further, the general method for encoding and decoding digital movingpicture signals has another drawback that if the GOB 102 including apicture in motion in relation to time cannot be decoded, a picturequality of the reproduced picture is largely degraded.

This problem will be described in more detail with reference to FIG. 5.FIG. 5 shows one frame including decoded signals of a moving picture,where a figure is moving in the center of the frame. In FIG. 5, a partmoving in relation to time is indicated by slanting lines, and theremaining part is a background which is still in relation to time. Ascene like this is general in TV conferences, TV telephones or the like.

Referring to FIG. 5, considering that any one of the first GOB 102 ₁through the fourth GOB 102 ₄ cannot be decoded. The first through fourthGOBs 102 ₁ through 102 ₄ include a picture still in relation to time. Ifthe second GOB 102 ₂ cannot be decoded, for example, a skillfuloperation is conducted to substitute the second GOB 102 ₂ of the presentframe 101 with the second GOB 102 ₂ of the preceding frame 101 ⁻¹ in thedecoding. With this operation, degradation of a picture quality in thesecond GOB 102 ₂ of the present frame 101 may be hardly detected.

However, it is a problem if decoding of the fifth through twelfth GOBs102 ₅ through 102 ₁₂ shown in FIG. 5 cannot be decoded. The fifththrough twelfth GOSs GOBs 102 ₅ through 102 ₁₂ include a picture movingin relation to time. This means, for example, that a picture in theninth GOB 102 ₉ of the preceding frame 101 ⁻¹ is largely different fromthe ninth GOB 102 ₉ of the present frame 101 in relation to time. If thedecoding of the ninth GOB 102 ₉ is unfeasible, degradation of thepicture quality of the ninth GOB 102 ₉ of the present frame 101 isobviously detected even if the skillful operation mentioned above isconducted in the decoding.

Accordingly, if decoding of GOB 102 including a picture moving inrelation to time becomes unfeasible, a quality of a reproduced pictureis largely degraded.

SUMMARY OF THE INVENTION

In the light of the above problems, an object of the present inventionis to provide a method for encoding and decoding digital moving picturesignals, which can appropriately decode subframes (GOBs) following asubframe in trouble in relation to time if a part of a bit stream ismissing or an error occurs in the bit stream.

Another object of the present invention is to provide a method forencoding and decoding digital moving picture signals, which can suppressdegradation of a reproduced picture to a small extent if decoding of asubframe (GOB) including a picture in motion in relation to time becomesunfeasible.

To accomplish the first object, the present invention is featured inthat in the method for encoding and decoding digital moving picturesignals of this invention, time position information representing anorder of displaying a subframe is attached to an identifier of thesubframe by which the subframe is identified.

According to the method for encoding and decoding digital moving picturesignals of this invention, time position information representing anorder of displaying a subframe is attached to an identifier used toidentify the subframe and the identifier of the subframe is encoded. Itis therefore possible to decode subframes following a subframe introuble appropriately in relation to time if a part of a bit stream ismissing or an error occurs in the bit stream by using the time positioninformation representing an order of displaying each of the subframesattached to an identifier used to identify the subframe

To accomplish the second object, the present invention is featured inthat in the method for encoding and decoding digital moving picturesignals of this invention, the number of blocks included in a subframeis varied according to a sum of quantities of generated information ofthe blocks included in the subframe so that each of all the subframesincluded in the frame has an equal sum of quantities of the generatedinformation of the blocks included in the subframe.

According to the method for encoding and decoding digital moving picturesignals of this invention, the number of blocks included in a subframeis varied according to a sum of quantities of generated information ofthe blocks included in the subframe so that each of all the subframesincluded in the frame has an equal sum of quantities of the generatedinformation of the blocks included in the subframe. In consequence, aspatial size of each subframe is not fixed. A subframe including a blockhaving a large number of coding bits is in a smaller size, whereas asubframe including a block having a small number of coding bits is in alarger size. It is therefore possible to suppress degradation of areproduced picture even if decoding of a subframe becomes unfeasiblesince a subframe including a block which includes a motion in relationto time and is difficult to be encoded is in a smaller size in relationto space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows units to be encoded in a general encoding method forencoding moving picture signals;

FIG. 2 shows a bit stream generated in the general encoding method forencoding moving picture signals;

FIG. 3 shows a GOB layer in the bit stream in FIG. 2 generated in thegeneral encoding method for encoding moving picture signals;

FIG. 4 illustrates an effect of a lack or an error of a part of a bitstream occurring in the general encoding and decoding method forencoding and decoding moving picture signals;

FIG. 5 illustrates an effect of a lack or an error of a part of a bitstream occurring in the general encoding and decoding method forencoding and decoding moving picture signals;

FIG. 6 shows a bit stream generated in a method for encoding digitalmoving picture signals according to first and second embodiments of thisinvention;

FIG. 7 is a flowchart illustrating the method for decoding digitalmoving picture signals according to the first embodiment of thisinvention;

FIG. 8 illustrates the method for encoding digital moving picturesignals according to the second embodiment of this invention; and

FIG. 9 shows a structure of subframes according to the second embodimentof this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, description will be made of embodiments according to thepresent invention referring to the drawings.

A method for encoding and decoding digital moving picture signalsaccording to a first embodiment will be now described, which maycorrectly decode a subframe as a unit in relation to time even if a partof a bit stream is missing or an error occurs therein.

In the encoding method according to this embodiment, one frame ofdigital motion picture signals is composed of, for example, 352×288pixels. The frame is divided into twelve subframes each composed of, forexample, 176×48 pixels. Further, the subframe is divided into thirtythree blocks 13 each composed of, for example, 16×16 pixels.

The encoding method according to this embodiment corresponds encodedinformation for one frame to a spatial hierarchical structure made up ofa frame 11, subframes 12 and blocks 13 to generate a bit stream 14 asshown, for example, in FIG. 6.

Meanings of encoded information of each layer shown in FIG. 6 are givenbelow: Frame layer 11S

FSC (20 bits): a frame identifier 15; a unique code by which a decodingmethod can be always identified, expressed as “0000 0000 0000 00010000”;

Subframe Layer 12S

SFSC (16 bits): a subframe identifier 16; a unique code by which adecoding method can be always identified, expressed as “0000 0000 00000001”;

SFNT (5 bits): a subframe time number 17; indicating a time position inwhich this subframe 12 should be displayed;

SFNS (4 bits): a subframe space number 18; indicating a spatial positionin which the subframe 12 should be displayed;

SFQUANT (5 bits): quantization characteristic information 19;representing a quantization characteristic when a block 13 in thesubframe 12 is encoded.

Incidentally, encoded information 20 in the block layer 13S which is thelowest hierarchy in FIG. 6 is generated in an encoding method of motiondetection, prediction, orthogonal transform, quantization, variablelength coding, etc., whose coding bit number are not fixed.

Now referring to FIG. 7, a decoding method according to this embodimentwill be now described. First, an FSC 15 which is an identifier of aframe layer 11S is found out from a bit stream 14 to establishsynchronization of the frame layer 11S.

After the establishing of synchronization of the frame layer 11S, anSFSC 16 which is an identifier of a subframe layer 12S is found out fromthe following bit stream 14 to establish synchronization of the subframelayer 12S. Then a subframe time number SFNT 17 and a subframe spacenumber SFNS 18 following the SFSC 16 are examined. Next, a bit stream 14of a block layer 13S is decoded. A method for decoding this block layer13S is a procedure to regenerate the block in processes of, for example,variable length decoding, reverse quantization, reverse orthogonaltransform, motion compensation, etc. Finally, the subframe 12 which is aset of the regenerated blocks 13 is placed in time and space positionsinstructed by the SFNT 17 and the SFNS 18. If synchronization of thedecoding is lost due to a lack of a part of the bit stream 14 or anerror therein, a seek for the SFSC 16 which is an identifier of thesubframe layer 12S is started. A lack or an error of a portion of, or anerror in, the bit stream 14 can be detected from, for example, that adecoded value exceeds a range specified in advance or an unexpected codeword appears when the bit stream 14 is decoded. When the SFSC 16 isdetected and synchronization of the subframe layer 12S is established,the SFNT 17 and the SNFS 18 are examined as stated above, the blocklayer 13S is decoded and regenerated, and the subframe 12 which is a setof the regenerated blocks 13 is placed in time and space positionsinstructed by the SFNT 17 and the SFNS 18.

According to the first embodiment of this invention, if a part of thebit stream 14 lacks is lacking or an error occurs in the bit stream 14,synchronization of the decoding is lost and the decoding becomesunfeasible, but correct decoding becomes possible immediately after asubframe 12 in trouble.

As having been described the above first embodiment by way of anexample, it is alternatively possible that the frame 11, the subframe 12and the block are in different sizes and shapes. A bit length of eachencoded information may be different from that of the above encodedinformation, or the frame layer 19 may be omitted, in addition.

According to a second embodiment of this invention, description will benow made of a method for encoding digital moving picture signals whichcan suppress degradation of a reproduced picture to a small extent if asubframe including a picture moving in relation to time cannot bedecoded. Incidentally, it is possible here to employ a decoding methodsimilar to that of the first embodiment.

In the encoding method of this embodiment, one frame 11 of digitalmoving picture signals is composed of, for example, 352×288 pixels. Theframe 11 is divided into blocks each composed of 16×16 pixels. In otherwords, one frame 11 is composed of 22 blocks×18 block lines 21. Theblock line 21 corresponds to the subframe 12 mentioned above.

In the encoding method of this embodiment, each block 13′ is encodedfrom the uppermost block line 21, as shown in FIG. 8, to generateencoded information. The encoded information of each block 13′ isgenerated in an encoding method of, for example, motion detection,prediction, orthogonal transform, quantization, variable length coding,etc., the number of coding bits of which is not fixed. Morespecifically, the number of coding bits of a block 13′ which isdifficult to be encoded is large, whereas the number of coding bits of ablock 13′ which is easy to be encoded is small. In the encoding methodof this embodiment, a set of blocks 13 or 13′composes a subframe 12 (ora block line 21) which is a unit of encoding, but the number of blocks13 or 13′ included in one subframe 12 or 12′ is not fixed.

A manner of generating a bit stream 14 in the encoding method of thisembodiment and a structure of a subframe layer 12S will be now describedwith reference to FIG. 6. When one frame is encoded, an identifier of aframe layer is encoded, and an FSC 15 is placed in a bit stream 14.Next, the identifier of the subframe layer 12S, a time number and aspace number of that subframe, and a quantization characteristic of thatsubframe are encoded together, and code words of an SFSC 16, and SFNT17, an SFNS 18 and an SFQUANT 19 are placed in the bit stream 14. At thesame time, block coding bit number integrated value B-add is set tozero. Following that, a block 13 is encoded and encoded information ofthe block 13 composed of variable codes is placed in the bit stream 14.Concurrently, the coding bit number B of this block 13 is added toB-add. Namely, an equation, B-add=B-add+B, is computed. Similarly,blocks 13 are encoded successively, encoded information 20 of each block13 is placed in the bit stream 14, and a calculation of B-add=B-add+B isrepeated each time. If the B-add exceeds a subframe interval SFd whenencoding of a certain block 12 is completed, an identifier of thesubframe, a time number and a space number of that subframe and aquantization characteristic of that subframe are encoded, and code wordsof an SFSC 16, an SFNT 17, an SFNS and an SFQUANT 19 are placed in thebit stream 14. At the same time, a block coding bit integrated valueB-add is set to zero. In other words, a new subframe layer 12S isstarted to be formed from that point.

The subframe interval SFd is set to, for example, 540 bits. Therefore,if one frame is encoded with, for example, 6400 bits in the encodingmethod of this embodiment, 12 subframes 12 exist in one frame since6400/540=11.85.

In the encoding method according to this embodiment, the number ofblocks 13 included in a subframe 12 is varied according to a quantity ofgenerated information of the blocks indicated in one subframe, therebyvarying a spatial size of the subframe 12, as stated above. Morespecifically, a subframe 12 including a block which is difficult to beencoded becomes small, whereas a subframe 12 including a block 13 whichis easy to be encoded becomes large. FIG. 9 shows an example of astructure of subframes formed in the encoding method of this embodiment.

According to th e the second embodiment of this invention, a subframe 12including a block 13 which contains a motion in relation to time, and isthus difficult to be coded is made smaller in relation to space. If suchsubframe 12 cannot be decoded, it is possible to suppress degradation ofa quality of a reproduced picture to a small extent. In a region withina frame in which no motion in relation to time exists and degradation ofthe picture quality is hardly detected even if the decoding isunfeasible, a size of one subframe is large in relation to space, whichallows a less volume of side information such as the subframe identifierSFSC 16, subframe number SFNT 16 and subframe number SFNT 17. This canprevent an encoding efficiency from being lowered.

As having been described the second embodiment by way of an example, itis alternatively possible that the frame 11, subframe 12 and the block13 are in different sizes and shapes. It is also possible to employvalues of a quantity of codes of one frame and a subframe interval SFDdifferent from those employed in the above example.

As obvious from the above embodiments, this invention enables correctdecoding of each subframe 12 as a unit in relation to time even if apart of the bit stream 14 is missing or an error occurs therein.

Further, according to this invention, it is possible to suppressdegradation of a quality of the reproduced picture to a small extent ifa subframe 13 including a block which is in motion in relation to timecannot be decoded.

Still further, in a region within a frame in which no motion in relationto time exists and degradation of a quality of the reproduced picturequality is hardly detected even if the decoding is unfeasible, sideinformation of the region is allowed to be in a small volume so that itis possible to prevent an encoding efficiency from being lowered.

1. A method for encoding digital motion picture signals of a frame,comprising the steps of: dividing said frame into plural blocks eachincluding N×M pixels; forming a subframe composed of a set of saidblocks, said subframe being a unit to be encoded; setting an identifierto said subframe to identify said subframe; and specifying a frame towhich said subframe belongs by adding to said identifier , the timeposition information representing an order of displaying said subframe;encoding said time position information along with said subframe, andmultiplexing said encoded time position information and a bit stream ofsaid encoded subframe to transmit said encoded time position informationand said bit stream.
 2. A method for encoding digital motion picturesignals of a frame, comprising the steps of: dividing said frame intoplural blocks each including N×M pixels; forming a subframe composed ofa set of said blocks, said subframe being a unit to be encoded; andvarying the number of said blocks included in said subframe according toa quantity of information generated by encoding each block to vary aspatial size of each of said subframes included in each frame.
 3. Amethod for encoding digital motion picture signals of a frame,comprising the steps of: dividing said frame into plural blocks eachincluding N×M pixels; forming a subframe composed of a set of saidblocks, said subframe being a unit to be encoded; setting an identifierto said subframe to identify said subframe; specifying a frame to whichsaid subframe belongs by adding to said identifier time positioninformation representing an order of displaying said subframe; encodingsaid time position information along with said subframe, andmultiplexing said encoded time position information and a bit stream ofsaid encoded subframe to transmit said encoded time position informationand said bit stream; and varying the number of said blocks included insaid subframe according to a quantity of information generated byencoding each block to vary a spatial size of each of said subframesincluded in each frame.
 4. The method for encoding digital motionpicture signals of a frame according to claim 2, wherein each of saidsubframes included in said frame has an equal sum of quantities ofgenerated information of said blocks included in said subframe.
 5. Themethod for encoding digital motion picture signals of a frame accordingto claim 3, wherein each of said subframes included in said frame has anequal sum of quantities of generated information of said blocks includedin said subframe.
 6. A method for encoding and decoding digital motionpicture signals of a frame, comprising the steps of: dividing said frameinto plural blocks each including N×M pixels; forming a subframecomposed of a set of said blocks, said subframe being a unit to beencoded; setting an identifier to said subframe to identify saidsubframe; specifying a frame to which said subframe belongs by adding tosaid identifier time position information representing an order ofdisplaying said subframe; encoding said time position information alongwith said subframe; multiplexing said encoded time position informationand a bit stream of said encoded subframe to transmit said encoded timeposition information and said bit stream; and decoding each of saidsubframes appropriately in relation to time by decoding and using saidtime position information to form said frame to said digital movingpicture signals.
 7. A method for encoding and decoding digital motionpicture signals of a frame, comprising the steps of: dividing said frameinto plural blocks each including N×M pixels; forming a subframecomposed of a set of said blocks, said subframe being a unit to beencoded; varying the number of said blocks included in said subframeaccording to a quantity of information generated by encoding each blockto vary a spatial size of each of said subframes included in each frame;and decoding each of said subframes to form said first of said digitalmoving picture signal.
 8. A method for encoding and decoding digitalmotion picture signals of a frame, comprising the steps of: dividingsaid frame into plural blocks each including N×M pixels; forming asubframe composed of a set of said blocks, said subframe being a unit tobe encoded, setting an identifier to said subframe to identify saidsubframe; specifying a frame to which said subframe belongs by adding tosaid identifier time position information representing an order ofdisplaying said subframe; encoding said time position information alongwith said subframe; multiplexing said encoded time position informationand a bit stream of said encoded subframe to transmit said encoded timeposition information and said bit stream; varying the number of saidblocks included in said subframe according to a quantity of informationgenerated by encoding each block to vary a spatial size of each of saidsubframes included in each frame; and decoding said subframeappropriately in relation to time by decoding and using said timeposition information to form said frame of said digital moving picturesignal.
 9. The method for encoding and decoding digital motion picturesignals of a frame according to claim 7, wherein each of said subframesincluded in said frame has an equal sum of quantities of generatedinformation of said blocks included in said subframe.
 10. The method forencoding and decoding digital motion picture signals of a frameaccording to claim 8, wherein each of said subframes include din saidframe has an equal sum of quantities of generated information of saidblocks included in said subframe.
 11. The method for encoding digitalmotion picture signals of a frame according to claim 1, wherein saidstep of adding time position information comprises adding the timeinformation to each subframe of said frame.
 12. The method for encodingdigital motion picture signals of a frame according to claim 11, furthercomprising the step of maintaining substantially constant a quantity ofinformation generated for each subframe within said frame thereby tovary spatial dimensions represented by each said subframe.
 13. Themethod for encoding digital motion picture signals of a frame accordingto claim 1, further comprising the step of maintaining substantiallyconstant a quantity of information generated for each subframe withinsaid frame thereby to vary spatial dimensions represented by each saidsubframe.
 14. The method for encoding and decoding digital motionpicture signals of a frame according to claim 6, wherein said step ofadding time position information comprises adding the time informationto each subframe of said frame.
 15. The method for encoding digitalmotion picture signals of a frame according to claim 14, furthercomprising the step of maintaining substantially constant a quantity ofinformation generated for each subframe within said frame thereby tovary spatial dimensions represented by each said subframe.
 16. Themethod for encoding digital motion picture signals of a frame accordingto claim 6, further comprising the step of maintaining substantiallyconstant a quantity of information generated for each subframe withinsaid frame thereby to vary spatial dimensions represented by each saidsubframe.